Every supplier listed in this thread is a re-seller. You will always get "off the street" pricing from these folks. You mention you only do about 3K a month... That's not enough to interest any service centers, unless you can possibly get an "in" with a sales rep.
A service center is loosely defined as an entity that has contracts directly with a mill, say USS Possco, or Cal Steel, which used to be Kaiser. They also mix in supply from offshore when suited.
To get a contract out of USS Possco or Cal is a major deal. I worked for an entity that consumed in excess of 180,000 tons a month in rolled product, and they couldn't get one. The steel industry is very tightly controlled from the top, and supply lines from the mill down are controlled by the mills themselves.
There are a few exceptions in Stainless and Aluminum, and Exotic Areospace products. But by and large, unless you have some pretty serious demand, you'll be dealing with re-sellers, i.e., retail. Even if you are a manufacturer, mostly due to credit demands, and Service Centers wanting to keep customer lists down to hi flow, low overhead volume buyers.
SoCal steel service centers.
Maas Hansen
Staub
Douglas
Reliance
Etc..
MetalWest is starting to make some inroads into SoCal.
Second Tier distributors (they buy from Service centers, and in some cases re-sell off the street).
Borrman
Industrial Metals
Tube Service
Coast Aluminum and Stainless
Bralco
Rolled Steel
Etc...
If you are a business, resale, start with Bormann and Industrial for plate. You're pricing will still be at least 30 to 50 percent higher than from a service center based on, say, 10 tons a week.
You guys getting tube, you have almost no choice, re-sellers. But it's not as bad as you would think. Re-sellers very often are dumping their stock rems off at or just below cost when you get really good pricing, which is good for guys off the street. If you need a consistent supply and price, well, then you run into trouble with them.
--ron